Polymer film with narrow molecular weight distribution and saran and laminates thereof

ABSTRACT

A film of ethylene vinyl acetate having a narrow molecular weight distribution and a saran composition that is a blend of emulsion and suspension polymerized saran or a saran composition that includes emulsion polymerized saran of the type generally considered suitable for liquid coating. A laminate including the film and composition and the method for production thereof including sequentially melt extruding tubular films of ethylene vinyl acetate which is irradiated, saran and ethylene vinyl acetate and then bubble orienting the three-ply laminate. The laminate is employed for packaging and forming packages of bone-in fresh red meat.

This is a division of application Ser. No. 129,501, filed Mar. 30, 1971,now U.S. Pat. No. 3,741,253.

BACKGROUND OF THE INVENTION

This invention relates to compositions for forming films, coatings, andlaminates formed from the compositions, methods for producing them andthe uses of the materials in packaging products, especially foodproducts such as bone-in fresh red meats.

In the past barrier laminates containing a barrier layer of sarantogether with layers of a copolymer of ethylene vinyl acetate with anouter layer of polyethylene have been used to package foodstuffsincluding meats as shown in U.S. Pat. No. 3,549,389. Other saran topolyethylene laminates and the like have also been known as shown byCanadian Pat. No. 743,021; and U.S. Pat. Nos. 3,031,332; 2,968,576 and2,955,869. However with such laminates it has generally been necessaryto employ bone puncture protective means such as those shown in U.S.Pat. No. 2,891,870. In addition, it may be seen that the laminates ofthe prior art have required separate plies to provide the necessaryabuse resistance of one lamina, the necessary adhesive characteristicsof still other laminas and the barrier properties of still anotherlamina or various special treatments to obtain suitable adhesioncharacteristics between the plies. In addition ethylene copolymershaving a substantial vinyl acetate content have not been believed to besatisfactory for an outer or inner lamina or coating that must be abuseresistant. Generally only those ethylene vinyl acetate copolymers havingvinyl acetate contents below 5% have been felt to be at all suitable forsuch use. These are only a few of the shortcomings of the prior art.

There is therefore a need for a laminate of simplified constructionhaving all the necessary characteristics for packaging bone-in cuts ofmeat and a wide variety of other items without the use of specialpackaging aids.

SUMMARY OF THE INVENTION

By an aspect of the invention a method for producing an abuse resistantpolymer film is provided that includes forming the film from a polymermaterial having a narrow molecular weight distribution with a generallyrandom molecular weight distribution therebetween. The general weightdistribution is preferably approximately that of the standard bellcurve. The preferred polymer material is based on ethylene vinyl acetatecontaining 5-20% vinyl acetate. More preferably the polymer is acopolymer of ethylene and vinyl acetate containing 8-12% vinyl acetate.

The above described polymer material is preferably formed into the outerply of a laminate. This outer ply could be an inside ply or coating in abag, for example, by outside ply it is meant that it is a surface orexposed ply that may be subject to external abuse, abuse by an objectengaging the coating. The laminate preferably includes an inside ply ofa barrier material, preferably one based on saran. The saran ispreferably a new saran composition comprising a polymer of vinylidenechloride having at least 50% vinylidene chloride and being a blend of5-40% suspension polymer and 60-95% emulsion polymer, peferably with anepoxy resin blended therewith in an amount of 2-10%.

An alternate inside barrier ply is a melt extruded layer of saran thatis a liquid coating grade of vinylidene chloride and vinyl chloridecopolymer having 5-15% vinyl chloride. In a preferred form the liquidcoating grade copolymer of vinylidene chloride and vinyl chloride ispresent in an amount of from 5-100% with the remainder being 2-10% epoxyresin and melt extrusion grade saran.

By another aspect of the invention improved films and laminates areprovided having the features described above with respect to the methodof their creation.

An aspect of the invention provides a very advantageous method ofmanufacturing a three-ply laminate having the inside barrier layer(described above) sandwiched between outside plies of the outer plydescribed above. By this method the third ply is melt extruded as atubular film, solidified and cross linked, preferably by irradiation ata dosage of 2-15 megareps. The irradiated tube is passed to a coatingdie where the second ply is melt extruded as a second tubular film,coated on and directly adhered to the irradiated tube forming a two-plytubular film. The two-ply tubular film is passed to a coating die,preferably while still hot, and the first ply is extruded as a tubularfilm coated on and directly adhered to the second tubular film forming athree-ply tubular film laminate. The three-ply tubular film issolidified and the tubing is stretched biaxially and thus biaxiallyoriented to provide a shrink tension of from 200-500 psi and a freeshrink of at least 40% at 205°F.

By still another aspect of the invention a method is provided forpreventing punctures and leaks in packaging bone-in cuts of meat in heatsealable plastic films. The method includes coating the inside of theplastic film that will be exposed to the cut of meat and bone with apolymer material that is solid at room temperature and has a narrowmolecular weight distribution. The meat is enclosed in the film to forma package and then heat is applied to the package to shrink the filmagainst the bone-in cut of meat.

It is therefore an object of this invention to provide compositions ofwide utility, having both advantageous manufacturing utility and end useutility, and providing end products that have not only wide utility butsuperior performance and low cost.

The invention may be better understood by reference to the followingdetailed description and drawings in which:

FIG. 1 is a schematic diagram of a preferred method for carrying out theinvention;

FIG. 2 is a cross section of the die head used in the present invention;

FIG. 3 is a view taken along line 3--3 of FIG. 2;

FIG. 4 is a cross sectional view of the laminate film of the presentinvention; and

FIG. 5 is a graph of molecular weights.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Unless otherwise identified specifically herein, percentage contentsrefer to the weight percent of each ingredient in the total compositionincluding all additives. Thus, when a composition includes additionalmaterials not affecting the "essential character" such as stabilizers,pigmenting agents, processing aids such as waxes, deodorizing agents,anti-static agents, anti-blocking agents, etc., these materials will beunderstood to slightly reduce the actual content of recited materialswhen they are given on the basis of their percentage content in thecomposition.

When a polymer material is set forth as being based on ethylene andvinyl acetate, this indicates that the ethylene and vinyl acetate arepolymerized but that other ingredients may be included in the polymer.Thus the polymer could be a terpolymer or some other polymer than acopolymer so long as the predominant polymer portions are those recited.The same is true of the saran or vinylidene chloride polymers. The term"saran" is used herein in its normal commercial sense with reference topolymers made by polymerizing vinylidene chloride and vinyl chloride.Additional monomers suitable for polymerization with the vinyl chlorideand vinylidene chloride to provide a barrier material are many and wellknown and therefore are not listed here. When a barrier layer isreferred to broadly, vinylidene chloride polymers are those mostcommonly used but in special instances other materials such as vinylchloride polymers, fluorocarbon polymers and many others may be used. Asis well known, many of the polymer materials, such as those referred to,include additives that are not considered to change the "essentialcharacter" of the material. A number of the additives are listed above.

Referring now to FIG. 1, a conventional extruder 9 is shown into whichis fed a polymer material having a narrow molecular weight distribution,preferably a polymer material based on ethylene and vinyl acetate having5-20% vinyl acetate, most preferably a copolymer of ethylene and vinylacetate having 5-20% vinyl acetate, more preferably 8-12% vinyl acetate.The molecular weight distribution of the polymer is preferably agenerally random molecular weight distribution most preferably in thegeneral distribution of the standard bell curve distribution which isrepresented by Line A of FIG. 5. It may be observed that this is not anexact bell curve which would be unusual in a commercial polymermaterial.

Molecular weight distribution as used herein is determined by use of agel permeation chromatograph. It has been found that a polymer havingthe molecular weight distribution of curve A in FIG. 5 is satisfactorywhile a polymer having a molecular weight distribution of curve B isunsatisfactory for the films of this invention. These curves wereanalyzed by standard statistical techniques and the followingdeterminations made:

                        Curve A Curve B                                           ______________________________________                                        standard deviation (sd)                                                                             3.07      3.65                                          Number Average Molecular                                                       Weight (M)           28.96     27.89                                         Coefficient of Variation                                                       (100) (sd)           10.62     13.08                                             M                                                                         Area under curve, ± 10% of M                                                                     64.32     50.72                                         ______________________________________                                    

Thus it has been found that a suitable polymer has a coefficient ofvariation which does not exceed 13. The number average molecular weightis the weighted average molecular weight which is the summation of themolecular weight shown on the abscissa of FIG. 5 times the number ofmolecules of a given weight represented by the per cent shown on theordinate.

More particularly it has been shown that for polymers having a numberaverage molecular weight of about 28 (curves A&B) that the area underthe distribution curve should be greater than that shown by curve B inan area bounded by an abscissa of + 10% of the number average molecularweight, a lower ordinate of o and the upper ordinates repesented by thedistribution curve. Preferably the area will be the similar area forcurve A less 50%, more preferably 25%, of the difference in these areasfor curve A and curve B. In other areas for polymers having a numberaverage molecular weight of about 28, the area is greater than 50.72,preferably greater than 57.57, more preferably greater than 60.94.

The tubing 10 is extruded downwardly from die head 11 which is fed fromextruder 9. The extruded tubing is 10-30 mils thick, more preferably15-25 mils thick. After coolng or quenching by water spray from coolingring 12, the tubing is collapsed by pinch rollers 13 and is fed throughan irradiation vault 14 surrounded by shielding 15 where it isirradiated with elctrons from an iron core transformer accelerator 16.Other accelerators such as a Vander Graff or resonating transformer maybe used. The radiation is not limited to electrons from an acceleratorsince any ionizing radiation may be used. The unit or radiation employedhere is the RAD which is defined as the amount of radiation which willdissipate 100 ergs of energy per gram of irradiated material by ionizingparticles. The MR is one million (10⁶) RAD.

In special instances it may be desirable to cross link the polymerthrough other means such as chemical cross linking agents. In thepreferred procedure, however, irradiation is employed and preferably asdescribed.

The time of irradiation of the ethylene vinyl acetate tubing 10 is notcritical but need only be enough to give the required dosage to effectthe desired amount of cross linking. In the pressent embodiment thetubing 10 is preferably irradiated at a dosage of 2-15 MR and morepreferably at a dosage of 2-10 MR.

The tubing 10 is guided through the irradiation vault 14 by rollers 17.After irradiation the tubing 10 goes through pinch rollers 18 followingwhich it is slightly inflated by a trapped bubble 20. The tubing is notsignificantly stretched longitudinally as the rollers 18 are driven atabout the same speed as rollers 13. The tubing is inflated only enoughto provide a substantially circular tubing without significanttransverse orientation.

The slightly inflated irradiated tubing 10 is passed through vacuumchamber 21 to a laminating or coating die 22. A second tubular film 23is melt extruded from the coating die 22 and coated onto and directlyadhered to the irradiated tube 10 to form a two-ply tubular film orlaminate 24. The second tubular film 23 is preferably a barrier ply. Thebarrier ply is preferably a polymer material based on saran or a polymerof vinylidene having at least 50% vinylidene and more preferably apolymer or copolymer of vinylidene chloride and vinyl chloride having5-40% vinyl chloride, most preferably 15-30% vinyl chloride. Thiscomposition is preferably 5-40% suspension polymer and 60-95% emulsionpolymer, more preferably 5-15% suspension polymer and 85-95% emulsionpolymer. The preferred barrier layer also includes in combinationtherewith 2-10% epoxy resin more preferably 4-6% epoxy resin. Thus thepreferred barrier layer is a saran film of a copolymer of vinylidenechloride and vinyl chloride having 5-40% vinyl chloride combined with2-10 % epoxy resin with the saran being a blend of from 5-40% suspensionpolymer and 60-95% emulsion polymer. The more preferred barrier filmwould be a saran that is a vinylidene chloride/vinyl chloride having15-30% vinyl chloride combined with 4-6% epoxy resin, the copolyer beinga blend of 5-15% suspension polymer and 85-95% emulsion polymer.

As used herein epoxy resin means a high viscosity thermoset resin asdistinct from epoxidized oils which are the usual epoxy plasticizers andare normally formed of epoxidized natural oil and are much less viscous.

It is quite unexpected that the blend of emulsion and suspension resins,particularly those of the saran or vinylidene type, can be melt extrudedand formed into a good quality biaxially oriented film. Normally thesuspension resin would be expected to cause gels to form in the emulsionresin during extrusion. In the present case, however, the suspensionpolymer seems to act as a stabilizer rather than causing gels in theemulsion polymer film. While we would not want to be held to thefollowing beliefs, it is believed that the suspension polymer melts moreslowly in the barrel of the extruder and acts as a scouring agent duringthe passage of the blend through the extruder preventing a build up ofthe saran on the extruder barrel and its decomposition. The emulsionpolymer tends to stick when it melts and the suspension polymer actssomewhat like ball bearings moving it along. Of course, prior toextrusion and adjacent the die the suspension polymer is also melted. Ithas been found that going above 20% in suspension polymer contentusually causes difficulty with film orientation. Only with very carefulhandling it is possible to go up to 40% suspension polymer content.Crystals form more rapidly in a suspension polymer film. Thus thesuspension polymer acts as a contaminant in the emulsion polymer in thesense that the suspension polymer crystallizes so rapidly that it doesnot permit sufficient time to achieve sufficient drawdown during theorientation step.

We have found it possible to operate at extrusion temperatures betweenthe normal processing conditions for the two polymers, in other wordsbetween 280°F and 340°F. It was not originally thought that the blendedmaterials would be compatible in the melted polymer state because of thedifferential melting rates between the two polymers.

Thus the extruder is preferably operated at a barrel temperature of200°-320°F, more preferably 250°-300°F and the extrusion die ispreferably operated at a temperature of from 280°-340°F more preferably295°-315°F. The extruded tubing is 1-5 mils thick, more preferably 2-4mils thick.

The extruder 25 is conventional, e.g., a standard 31/4 inch extruder.The die 22 is a circular cross head die which has an adaptor 26 (FIG. 2)attached thereto to provide in its preferred form a 31/2 inch opening 27for the slightly inflated tubing 10.

The details of the die 22 may be better appreciated by referring toFIGS. 2 and 3. The opening 27 through which the inflated substratepasses has been formed through mandrel 28 which is attached to the diehousing 29. The path of the molten coating material 23 is indicated bythe arrows in FIGS. 2 and 3. The vacuum chamber 21 puts a mild vacuum,e.g., in the range of from 0 to about 25 inches of water, on the die 22to draw or pull up the extruded film 23 while it is still molten againstthe inflated tubing 10 to prevent the formation of occluded bubbles inthe laminate 24. The vacuum chamber 22 can simply consist of thecylindrical housing whose inner diameter closely conforms to the outerdiameter of the inflated tubing. A vacuum can be applied through outlet30 by a conventional vacuum hose.

An alternate preferred barrier material is a saran liquid coatingmaterial of the type used to solvent or emulsion coat with saran ratherthan melt coat. This material can be substituted for the suspensionpolymerized saran of the previously described preferred barriercomposition. It is believed that this liquid coating vinylidene polymermaterial acts in exactly the opposite manner from the suspension polymersaran, it has a lower melt viscosity and enhances the blend's flow inthe manner of a lubricating effect. Liquid coating sarans are notthought of as being melt extrudable. In still other instances it hasbeen found possible to substitute the liquid coating saran for all ofthe saran in the composition and melt extrude the composition and form agood film which has indeed been surprising. The liquid coating saransare also usually emulsion polymerized but have established a distinctivecharacter in the art.

The two-ply film 24 is passed to the coating or laminating die 32preferably while still hot. In a discontinuous process it would bepossible to cool or quench the tubing 24 prior to passing it to thesecond coating die 32 but this would also necessitate, in the usualinstance, both a reinflation and a reheating of the tubing to obtain anexcellent bond between the second ply and the first ply. The first plyconsidering the tubing from the outside thereof would be both an outerply and the outer ply of the tubing.

A first tubular film, the third extruded in sequence, is melt extrudedfrom the coating die 32 and coated on and directly adhered to thetwo-ply film 24 to form a three-ply tubular film 34. Tubular film 33 ispreferably of a composition chosen from those given when discussingtubular film 10 above. Although not necessarily of the same identicalcomposition as tubular film 10, it would normally be identical as amatter of convenience in compounding. It may be seen that the coatingprocess at die 32 is the same as that at die 22. The vacuum chamber 36serves the same function as the vacuum chamber 21 and operates in thesame manner with a vacuum being applied through outlet 37. The tubularfilm or ply 33 is 3-15 mils thick, more preferably 4-12 mils thick.

The three-ply tubular film laminate 34 is cooled or quenched by thewater spray from cooling ring 39. The water is normally at about 45°F.Pinch rollers 40 then collapse the three-ply tubular film and the filmis rolled onto wind-up roll 41. Alternatively in a continuous processthe film would not be rolled up onto wind-up roll 41 but would bedelivered directly to the next step in the process sequence to stretchthe film.

As shown in FIG. 1 a pay-out roll 42, which would be a previouslyprepared wound-up roll 41, is unwound over guide roll 43. The laminate34 is substantially unstretched and unoriented as it passes over theguide roll 43. The film passes from guide roll 43 into a hot water bathtank 44 containing water 45. The preferred reheating temperature or hotwater temperature is 160°-212°F, more preferably 180°-205°F. Thecollapsed three-ply tubular film is submerged in the hot water for aretention time of at least about 5 seconds. This is generally necessaryto bring the film up to the desired temperature for orientationstretching. A typical retention time in the water bath is about 20seconds. Guide rolls and 47 guide the collapsed tubing through the waterbath 45.

After the temperature of the three lamina of the tubing are adjusted totheir proper orientation level, the bubble 46 is blown and the film isstretched in both the transverse and longitudinal directions in apreferred ratio of 1:1.5-1:6, more preferably 1:2-1:4 which would be abiaxial orientation of 1:2.25-1:3.60 and 1:4-1:16, respectively. Each ofthe coatings and the substrate are reduced substantially in equalproportions. It may be seen that the laminate is orientable out of hotwater to produce the desired physical characteristics. The bubble 46 ismaintained between pinch rolls 48 and 49. The tubing is collapsed byrollers 50 and the laminate is conveyed through pinch rollers 49 andacross guide roll 51 and rolled onto wind-up roll 52. Idler roll 53assures a good wind up.

In FIG. 4, a cross section of the laminate 34 is illustrated, showingthe third protective outer ply of plastic film 10 which is of course theintermediate ply of the tubing, barrier layer coating or inside ply ofplastic film 23 and the first ply or coating of plastic film 33 whichforms an outer protective ply for the laminate and outer protectivecoating of the tubular member. These three plies are directly joinedwithout intermediate plies to form the three-ply laminate. Thecompositions of these plies will not be repeated here as they are clearfrom the previous description. After orientation the laminate film,which is shown in FIG. 4, has a prefered thickness of the third ply 10of 0.5 to 5 mils, more preferably 1 to 2 mils, thickness of theintermediate ply 23 of 0.052-2 mils, more preferably 0.1-0.5 mils and athickness of the outer ply 33 of 0.1-4 mils, more preferably 0.25-1mils. The laminate has a preferred shrink tension of from 200-400 psiand a free shrink of at least 40% more preferably at least 50%, at 205°Fand a free shrink of at least 20%, more preferably at least 30%, at185°F.

In another preferred procedure of producing the laminate, the second andthird applied coatings can be coextruded onto the preformed tubing froma coextrusion die. This would produce the same end laminate but is asomewhat more difficult procedure.

The tubular film produced from the tubing of this invention produces anexcellent barrier bag, the ply 10 bonding to itself very well attemperatures between 200°F and 350°F without distorting substantiallywhen the seals are produced with a thermal impulse sealer.

The ply 10 also gives excellent puncture strength. The thin saran basedbarrier layer provides the necessary barrier characteristics with aminimum thickness and expense. The outer layer of unirradiatedpolyethylene copolymer give high low temperature abuse resistance andimproved tear resistance.

An advantageous method for employing bags made from the tubing of thisinvention is shown in U.S. Pat. No. 3,552,090. The bags are suitablyclosed after vacuumizing by clipping, for example, as shown in U.S. Pat.No. 3,383,746. A suitable vacuumizing device is shown in U.S. patentapplication Ser. No. 844,883, filed July 25, 1969, Dave L. Owen,inventor now U.S. Pat. No. 3,628,526. The just referred to patents andapplications are all assigned to the same assignee as the presentapplication.

The laminate's optimum use and the use for which it was specificallydesigned, although it obviously would have many other uses, is as apackaging material for bone-in cuts of fresh red meat having exposedbones. When so employed the preferred and the most preferred laminatewhich is formed of the preferred and most preferred compositions is ofalmost critical importance. While an inferior laminate could be usedemploying for example a different barrier layer, this is at asubstantial cost in processing ability and quality. The laminate is alsonontoxic and food approved. It will be understood that when a bag isemployed to package a piece of fresh red meat that has not been frozenand is not to be frozen but will be packaged and retained at lowtemperatures, e.g., 32°-45°F, the laminate encloses the bone-in cut ofmeat and exposed bones impinge against the inside protective ply of thebag which is an outside protective ply of the laminate.

In the preferred process, the bone-in meat is inserted into thethree-ply laminate which is biaxially oriented and heat shrinkable. Thelaminate thus encloses a bone-in cut of meat and depending on the cut ofmeat may always be impinged against by an exposed bone. The bag isevacuated and sealed about the meat to preserve the vacuum. The bag isthen heat shrunk taut on the meat and with the bone-in cut of meat formsa package that will preserve the meat for an extended period of time.

This invention provides an excellent means of preventing punctures andleakers in packaging bone-in cuts of meat in heat shrinkable plasticfilms because the inside coating of the plastic film which is exposed tothe meat and bone is a polymer material having a substantial narrowmolecular weight distribution that is solid at room temperature. Thepreferred polymer material for this coating is the composition givenwith respect to the first ply already described. By enclosing the meatin this film and forming a package and then applying heat to the packageto shrink the film against the bone-in cut of meat, an excellent packagecan be formed. by using such a film with a good barrier layer, the meatmay be protected in storage for extended periods of time.

In the preferred form of this invention, it is important that theirradiation dosage be within the confines set because this yields anadherent coating that has sufficient tensile strength to give goodprocessability, good bone-puncture resistance and good orientability.Irradiation should be sufficient to increase the tensile strengthwithout deteriorating elongation very much, as the material must stretchwith the bone when packaging bone-in cuts of fresh red meat. At the sametime it is desirable that the bag cling to soft meat and to bonewherever the bone sticks out of the meat. Fresh red meat can be soft andallow the bone to move or "float" within it. If the film is irradiatedtoo much, the elongation goes down and the bone will go right through onimpact. If the vinyl acetate content is above that specified, themelting point of the polymer decreases adversely affecting the hightemperature properties required for shrink packaging.

In addition to losing abuse resistance at shrink tunnel temperatures,the seals delaminate when the vinyl acetate content goes up much above18% on this particular laminate. If the vinyl acetate drops down below5%, the low temperature elasticity decreases and the modulus ofelasticity increases to such an extent that the bag no longer functionsas required for an efficient packaging operation.

The laminate has a number of very desirable characteristics, in itspreferred form, including good shrinkability at a moderately raisedtemperature an elongation of at least 50%, more preferably 100-125%, anoxygen transmission rate of no more than 70 cc/(1 sq.m./24 hrs./1 atm.)at 73°F, 0% r.h. (A.S.T.M. D 1434); and more preferably no more than 25cc/(1 sq.m./24 hrs./1 atm.) at 73°F, 0% r.h. (A.S.T.M. D 1434). In itspreferred form the film has a ball burst impact resistance of at least25 cm-kg.

Various aspects of the invention can be employed independently or inother combinations with advantage over the materials normally soemployed. The saran compositions can be formed into independent films.The compositions have the superior extrusion characteristics alreadyenumerated whether being melt extrusion coated or melt extruded asindependent self supporting films. Of course, to be self supporting theextruded saran film would have to be at least about 2-3 mils thick ifextruded as a tubing using normal saran tube extrusion techniques. Inaddition it has been found that the saran film formed from a blend ofemulsion and suspension polymerized saran has unexpected tear andpuncture resistance for an oriented film when compared to existing knownsaran films.

In certain instances it might be desirable to substitute another polymerfor the outer laminate or ply in a bag. This is the ply that needs to beresistant to scuff and tear abuse as against puncture resistance whichis important for the inside ply of the preferred bag to be used inpackaging bone-in fresh red meat. These polymers should also haverelatively narrow molecular weight distributions, preferably with agenerally random molecular weight distribution, most preferably in thegeneral distribution of the standard bell curve. Examples of suchpolymers are polypropylene, polyamids, polyesters and the like, andcopolymers, terpolymers and other polymers of such materials. Suchgroups of coating polymers are well known, however, the proper choosingof the polymer material with the right molecular weight characteristicsis an aspect of this invention. Of course, in certain applications theouter lamina or even the inner lamina might not need the advantages ofthis invention but the other lamina may be necessary and so the aspectsof the invention are claimed both in the combination essential for bestquality for the preferred application and independently for otherapplications or uses.

This invention is further illustrated by the following example:

EXAMPLE I

Following the procedure as schematically outlined in FIG. 1, an ethylenevinyl acetate copolymer containing 10% vinyl acetate having a melt indexof about 2 and a molecular weight distribution as shown by line A ofFIG. 5 and sold as UE 637 by U.S. Industrial Chemicals Division ofNational Distillers, is fed into the extruder hopper of extruder 9. Theextruder is a 3.5 inch extruder and is operated at the followingtemperatures: rear zone, 250°F; mid-barrel 270°F; front barrel, 290°F;adaptor, 300°F; and die, 330°F. The screw rpm is 37 and the pressure is3,800 ps. The die diameter is 3.5 inches and the tubing circumferenceproduced is 8 inches. The water from the cooling ring 12 is 45°F. Thepinch rolls 13 are operated at 35 feet per minute and the tubingthickness is approximately 18 mils.

The collapsed tubing is passed through an irradiation unit such as thatdepicted in FIG. 1 operated at 500 KEV, 20 MA and a speed of 35 feet perminute. Four passes are made and the tubing receives a dosage of about 6megarads.

The irradiated substrate film is then passed to a coating die 22 whereit is coated with a barrier material. The composition of the barrierlayer is a lightly plasticized copolymer of vinylidene chloride andvinyl chloride. The copolymer is a mixture of 10% suspension polymerizedand 90% emulsion polymerized copolymer. The emulsion polymerizedcopolymer consists of about 70% vinylidene chloride and 30% vinylchloride and the suspension polymerized copolymer consists of about 80%vinylidene chloride and 20% vinyl chloride. These materials werepurchased from Dow Chemical Company and are sold as UP 925 (emulsionpolymerized resin) and SP 489 (suspension polymerized resin). Thecomposition includes 5% of an epichlorohydrin/bisphenol A epoxy resinsold as EPON resin 828 by the Shell Chemical Company. It also includesabout 0.5% of a microcrystalline paraffin wax purchased from SunChemical Company and sold as Wax 5512. The three resins are blended in ahigh speed, high intensity Prodex-Henschel blender and the blend is fedinto the hopper of extruder 25 which is a 2 inch Prodex extruderoperated with a cross head die of the type illustrated in FIGS. 2 and 3.The second extruder is operated at the following temperatures: rearzone, 210°F; mid-barrel, 260°F; front barrel, 300°F; adaptor, 285°F; anddie 320°F. The screw rpm is 34 and the pressure is 5,500 psi. The diediameter is 3.5 inches and the tubing circumference is 8 inches. The toprolls 18 are operated at 35 fpm and the coating thickness isapproximately 3 mils.

The second coating resin applied at extruder 35 is identical to theresin added to the hopper of the first extruder 9 and the extruderoperating conditions are rear zone, 250°F; mid-barrel, 270°F; frontbarrel, 380°F; adaptor, 440°F; and die 450°F. In other respects theextruder's operation is the same as that set for extruder 9. The coatingdie 32 is of the same design as the coating die 22. The bottom rolls 40are operated at 36 fpm and the water from the chill ring 39 is at 45°F.The coating thickness is approximately 6 mils.

Biaxial orientation is carried out by preheating in water at about 190°Fas shown at 44 of FIG. 1 and passing the thus heated tubing throughpinch rolls operating at 19 fpm to deflate rolls operating at 70 fpm andblowing the 4 inch wide tubing to produce a film width of approximately16 inches with a film thickness of approximately 2.4 mils. This tubingis then rolled up on a storage roll which is then converted into bags bysealing the tubing transversely at intervals to form bottoms inconventional manner and severing the tubing into desired bag lengths.

EXAMPLE II

The above procedure was repeated except the barrier layer was varied bythe addition of 2% of 2-ethyl hexyl diphenyl phosphate plasticizerpurchased from Monsanto and identified as Santicizer 141 and reducingthe epoxy resin content to 3%.

EXAMPLE III

The procedure of Example I was repeated except the barrier layercomposition was 66% saran resin UP 925, 30% of a liquid coating saranresin purchased from Dow Chemical Company and sold as QX 2168, 2% Eponresin 828 and 2% Santicizer 141.

EXAMPLE IV

The procedure of Example III was repeated except the saran in thebarrier layer composition was all QX 2168.

EXAMPLES V & VI

The procedures of Examples III and IV were repeated except a liquidcoating saran sold by W. R. Grace & Co. as Daran CR 6795-H wassubstituted for the QX 2168.

EXAMPLE VII

The procedure of Example I was repeated except 5% of an epoxidizedsoybean oil (not an epoxy resin as defined herein) sold by Swift & Co.as Epoxol 7-4 was substituted for the 5% epoxy resin.

EXAMPLE VIII

The procedure of Example VII was repeated except 4% of 2-ethyl hexyldiphenyl phosphate plasticizer and 1% magnesium oxide were substitutedfor the 5% epoxy resin.

EXAMPLE IX

The procedure of Example I was repeated except a mixture of 53.3% byweight of isotactic polypropylene (Novamont* F007), 33.3% polybutene-1(Mobil* PB 103) and 13.3% atactic polypropylene ("Novamont" Lot 2030) isused to form the third layer. The atactic and isotactic polypropyleneare first added in proper proportion to a banbury mixer and melt blendedfor approximately 8 minutes at 400°F. and then extruded into a sheetwhich is diced into pellets. These pellets are combined with pellets ofpolybutene-1 in a rotating drum and this admixture is charged to thehopper of extruder 35. Extruder 35 is operated at the followingtemperatures: rear zone, 385°F; mid-zone 400°F, forward zone, 450°F;adaptor, 400°F; and die, 425°F.

EXAMPLE X

The saran composition of Example II was extruded as a self supportingsingle layer film under the extrusion conditions set forth in Example IIexcept 4% of the epoxy resin was used, and the UP 925 resin content wasreduced 1%, and interior coating of propylene glycol was appliedinteriorly to prevent sticking when the tubing is collapsed prior to itsbiaxial orientation and the process was continuous, the bubble 46 beingformed after collapse but without rolling the tubing up. In addition,the water bath was maintained at about 100°F, the extrusion gauge atabout 5 mils and the biaxially oriented gauge at about 0.75 mils after atotal orientation stretch ratio of about 12:1 biaxially. The film wasfound to have unexpected tear and puncture resistance for an orientedfilm when compared to existing known saran films.

PACKAGE ABUSE TESTS

The following test procedure was carried out, all test bags wereprecoded and conditioned for 24 hours at 45°-50°F. The bags arerandomized and used to package full bone-in ribs weighing 25-30 pounds.The bags are 16 inches wide by 30 or 32 inches deep. The packages werevacuumized, clipped, shrunk and dried in an air blast. The packages areboxed in wax-coated corrugated shipping containers, three to acontainer. The shipping containers are then closed with nylonmonofilament tape.

In the drop test the individual containers are dropped from a height ofthree feet from a moving conveyor. In the simulated motor freightshipment the containers are stored at 38°F for 24 hours and then shakesfor 7.5 minutes at 1 g. on a L.A.B. Vibration tester* -- sincrenoismotion -- to simulate a 125-mile truck shipment.

In both tests the packages are pumped with air and submerged under waterto determine leakage which is rated as failure.

                                      TABLE I                                     __________________________________________________________________________              LAMINATE                                                                             BONE PUNCTURE RESISTANCE                                                                       SHIPPING ABUSE (BONE-                                                                       OXYGEN BARRIER                BAG       GAUGE  % SURVIVAL       IN) % SURVIVAL                                                                              cc(1 sq.m./24 hrs./1          __________________________________________________________________________                                                    atm.                          Made in Substantial                                                           Conformance with                                                                        2.4    75%              82%           45                            Example I                                                                     Made in Substantial                                                           Conformance with                                                                        2.7    73%              92%           40-45                         Example I                                                                     Made in Substantial                                                           Conformance with                                                                        2.0    63%              80%           35                            Example II                                                                    Standard Saran Bag                                                            Produced by                                                                             1.9    25%              45%           150                           W. R. Grace & Co.                                                             Standard Saran Bag                                                            Purchased from    23.3%            36.6%        150                           Union Carbide                                                                 __________________________________________________________________________

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method for producing alaminate comprising:A. melt extruding a copolymer of ethylene and vinylacetate through an annular die to form a first tubulr film, saidcopolymer having 5 to 20% vinyl acetate and with the number averagemolecular weight of said copolymer having a coefficient of variation notexceeding 13, B. irradiating said first film to cross link saidcopolymer, C. inflating said first tubular film without causingsignificant transverse orientation to provide a substantially circulartubing, D. blending 5 to 40 weight percent of suspension polymerizedcopolymer of vinylidene chloride and vinyl chloride and 60 to 95 weightpercent of emulsion polymerized copolymer of vinylidene chloride andvinyl chloride to form a first blend, the vinyl chloride content of saidcopolymers being in the range of 5 to 40 percent, E. blending 2 to 10weight percent of epoxy resin with said first blend to form a secondblend, F. melt extruding said second blend through a second annular dieto form a second tubular film on said irradiated first ply to form a twoply tubular film, said second film providing oxygen barrier propertiesso that the laminate has an oxygen transmission rate of no more than 70cc/sq m/24 hrs/1 atm. at 73°F., and G. melt extruding a third tubularfilm of a copolymer of ethylene and vinyl acetate through an annular dieonto said two ply tubular film and forming a three ply tubular film. 2.The method of claim 1 wherein said three ply tubular film is stretchedto effect biaxial orientation of each ply.
 3. The method of claim 2wherein said three ply tubular film is biaxially oriented by submergingit in water at 160 to 212°F for at least 5 seconds and blowing a bubblein the tubing out of the water to stretch the tubing longitudinally andtransversely in a ratio of 1:1.5- 1:6.
 4. The method of claim 1 whereineach of said plies are directly joined to the adjacent plies without anintermediate ply.
 5. The method of claim 1 wherein said two ply film ispassed to a coating die for the application of the third tubular filmwhile said two ply film is hot.
 6. A method for producing a laminateadapted for vacuum packaging bone-in fresh red meat comprising meltextruding a copolymer of ethylene and vinyl acetate having 8-12% vinylacetate through annular die so as to form a first tubular film, thenumber average molecular weight of said copolymer having a coefficientof variation not exceeding 13, and said extruded tubing being 15-25 milsthick; quenching said first tubular film; irradiating said first tubularfilm at a dosage of 2-10 megarads; inflating said film without causingsignificant transverse orientation to form a substantially circulartubing; passing said irradiated, inflated first film to a coating die;melt extruding through a second annular die a second tubular film of acopolymer of vinylidene chloride and vinyl chloride having 15-30% vinylchloride combined with 4-6% epoxy resin, said copolymer having beenprepared by blending a mixture of 5-15% suspension polymer and 85-95%emulsion polymer, and the copolymer having a temperature of 295 to 315°Fat the die, and said second tubular film being 2-4 mils thick; coatingsaid irradiated first tubular film with said second tubular film throughan annular die and forming a two-ply tubular film; passing said two-plyfilm to a coating die while still hot; melt extruding a third tubularfilm of a copolymer of ethylene and vinyl acetate having 5-20% vinylacetate and said tubing being 4-12 mils thick; coating said two-plytubular film with said third tubular film through an annular die andforming a three-ply tubular film; quenching said three-ply tubular film;collapsing said three-ply tubular film; submerging said collapsedthree-ply tubular film in water at 180° to 205°F for at least about 5seconds; blowing a bubble in the tubing out of said water and stretchingthe tubing longitudinally in a ratio of 1:2-1:4 and transversely in aratio of 1:2-1:4.